1. Field of the Invention
The invention relates to micromagnetic components for power applications.
2. Discussion of the Related Art
There is an increasing market for compact and efficient portable electronic devices such as notebook computers and cellular telephones. This increasing market has established the need for both a reduction in size and an improvement in efficiency in the associated power integrated circuits. Specifically, to reduce power consumption and increase battery life, integrated power management is being sought, e.g., single-chip power components such as on-chip DC-DC converters. An essential aspect of such integration is the merging of CMOS and magnetic elements onto a single chip. In particular, planar inductors and transformers, operated at high frequencies, are the fundamental magnetic elements of such DC-DC converters. In addition, current magnetic materials used in inductors and transformers, e.g., Permalloy, suffer from some limitations that would be undesirable for such on-chip power devices. For example, Permalloy""s adherence tends to be less than desired, and the alloy has some limitations in frequency range due to its electrical conductivity.
Thus, improved techniques for forming micromagnetic components for integrated CMOS/power applications, as well as improved materials for such components, are desired.
The process of the invention involves forming multilayer components in which a photoresist-type material is used not only as a conventional patterning material, but also as an insulating and/or planarizing material between magnetic or electrically conductive layers. This use of photoresist as part of the overall component structure is unique to LIGA-type processes. (LIGA is a German acronym that stands for, in English, lithography, plating, molding. See, e.g., H. Guckel, xe2x80x9cMicromechanics for x-ray lithography and x-ray lithography for micromechanics,xe2x80x9d Precision Engineering and Opto-Mechanics, SPIE, Vol. 1167, 151-158 (1989) for a general discussion of LIGA processes.) According to the invention, a variety of integrated CMOS/micromagnetic components are capable of being formed, including components containing planar inductors and transformers. Additionally, in one embodiment of the process, a particular technique is used to etch gold-containing seed layers from a substrate surface without damaging an electroplated copper coil. Such a technique is useful when electroplating copper onto such a seed layer, because most chemicals used to etch away the gold will, in the absence of such a technique, damage the copper coil.
The invention also relates to a magnetic material particularly useful in devices such as inductors and transformers. The material is an amorphous iron-cobalt-phosphorus alloy having a composition of CoxPyFez, where x+y+z=100, x is 5 to 15, y is 13 to 20, and z is the remainder. In one useful embodiment, x is 11 and y is 17. The cobalt and iron provide relatively high saturation magnetization and low coercivity, while the phosphorus is present in an amount that provides an amorphous structure, but does not unacceptably lower the saturation magnetization. The alloy typically exhibits a coercivity of 0.1 to 0.5 Oe, an electrical resistivity of 100 to 150 xcexcxcexa9-cm, and a saturation magnetization of about 16 to about 19 kG, all of which represent improvements over Permalloy.